I have two firearms using the 375 wcf. A Marlin and a Thompson Center Contender with a 14" ported barrel.
I use the same load for both the rifle and handgun with AA 1680 powder and the 220 Hornady slug. The Marlin will print in a MOA and the Contender comes very close.
I've never gotten a deer with the Contender but the Marlin did a good job on a small buck. at 70+/- yards. I bought a bag of 200 375WW brass and 2 boxes of 20 each WW unprimed brass at a gun show, both were years ago in the early '90s. I've not needed any more since then as the brass seems to last forever with only a little trim needed after 4-5 loads. To find brass, I would try as many gun shows with the guys who have boxes of old ammo and brass... you never can tell.
